Bernard Perrin

Granular avalanches in fluids.

Three regimes of granular avalanches in fluids are put in light depending on the Stokes number St which prescribes the relative importance of grain inertia and fluid viscous effects and on the grain/fluid density ratio r. In gas (r>>1 and St>1, e.g., the dry case), the amplitude and time duration of avalanches do not depend on any fluid effect. In liquids (r approximately 1), for decreasing St, the amplitude decreases and the time duration increases, exploring an inertial regime and a viscous regime. These three regimes are described by the analysis of the elementary motion of one grain.

Application of the picosecond ultrasonic technique to the study of elastic and time-resolved thermal properties of materials

Abstract We describe a technique — the Picosecond Ultrasonic Technique — making use of a femtosecond laser source, suitable to generate and to detect high frequency elastic waves in submicron samples. The optically-generated acoustic pulse has a broad spectral contents extending over several hundreds of GHz. Then, we present results obtained in thin layers and in bulk samples as well. Using this technique, we were able to measure thickness variations of a few nanometers in a 100 nm thick LiNbO 3 sample. We present also results obtained in a set of periodic Cu/W multilayers. In these samples, we measured the effective sound velocity of the bulk longitudinal modes propagating within the heterostructure as a function of the superlattice period. For the shortest periods, we observe a decrease of the sound velocity by ~ 10%, corresponding to a softening of the heterostructure. This elastic anomaly is related to interfacial effects. Then, we were able to put in vibration the surface of Cu/W multilayers at frequencies up to 0.81 THz. We attribute this vibration to a surface mode localized in the second frequency band gap of the dispersion curve. Finally, we show how time-resolved thermal properties can be deduced from a picosecond ultrasonic experiment and we present results obtained in a macroscopic aluminium sample.

INTERFEROMETRIC DETECTION IN PICOSECOND ULTRASONICS

Abstract We report results obtained using an optical interferometric detection in picosecond ultrasonics. A comparison between signals detected by reflectometric and interferometric measurements was done in various systems: thin films, multilayers and particles in colloids.

Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in a diamond anvil cell: application to the stability study of AlPdMn.

We report an innovative high pressure method combining the diamond anvil cell device with the technique of picosecond ultrasonics. Such an approach allows us to measure sound velocity and attenuation of solids and liquids under pressure of tens of GPa, overcoming all the drawbacks of traditional techniques. The power of this experimental technique is demonstrated in studies of lattice dynamics and relaxation processes in a metallic single grain of AlPdMn quasicrystal, and in rare gas solids neon and argon.

Wall effects on granular heap stability

We investigate the effects of lateral walls on the angle of movement and on the angle of repose of a granular pile. Our experimental results for beads immersed in water are similar to previous results obtained in air and to recent numerical simulations. All of these results, showing an increase of pile angles with a decreasing gap width, are explained by a model based on the redirection of stresses through the granular media. Two regimes are observed depending on the bead diameter. For large beads, the range of wall effects corresponds to a constant number of beads, whereas it corresponds to a constant characteristic length for small beads as they aggregate via van der Waals forces.

Coherent generation of acoustic phonons in an optical microcavity.

Ultrafast coherent generation of acoustic phonons is studied in a semiconductor optical microcavity. The confinement of the light pulse amplifies both the generation and the detection of phonons. In addition, the standing wave character of the photon field modifies the generation and detection phonon bandwidth. Coherent generation experiments in an acoustic nanocavity embedded in an optical microcavity are reported as a function of laser energy and incidence angle to evidence the separate role of the optical and exciton resonances. Amplified signals and phonon spectra modified by the optical confinement are demonstrated.

PHOTOTHERMAL PROPERTIES OF BULK AND LAYERED MATERIALS BY THE PICOSECOND ACOUSTICS TECHNIQUE

The picosecond acoustic technique is a pump and probe method associated with a lock-in amplification scheme. It involves the excitation of the sample by an ultrashort optical pulse and the monitoring of the subsequent relaxation processes by a weaker pulse delayed with respect to the former. In particular, information about the temperature evolution a short duration after the pump pulse is absorbed can be obtained. We examine here the different time scales involved in such an experiment. We show that the photothermal signal is superimposed on a continuous background originating from the modulation of the pump beam for synchronous detection. We also derive expressions for the cooling rate of both bulk and layered specimens after an instantaneous heating and we show experimentally that this macroscopic approach is valid after a delay of several picoseconds.

Subterahertz monochromatic acoustic wave propagation using semiconductor superlattices as transducers

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Sub-Terahertz Monochromatic Transduction with Semiconductor Acoustic Nanodevices Agnès Huynh, Bernard Perrin, N. D. Lanzillotti Kimura, Bernard Jusserand, A. Fainstein, Aristide Lemaitre

Artificial enzymic membrane pump for glucose transport against its chemical gradient

An artificial glucokinase/phosphatase porous membrane separating two unequal compartments of a diffusion cell was used to pump glucose from one compartment against the concentration gradient of the opposite one. Our results mainly demonstrate that, a kinase/phosphatase reactional sequence acting on both parts of a pore structure and necessarily in unstirred layers may pump a neutral solute from one compartment against the concentration gradient of the opposite one without any detectable pollution of the charged intermediary product. The corresponding theoretical analysis, which underlines the key role played by the diffusion layers located on both parts of this bienzymic membrane and the membranes charge effect, was found in good agreement with the experimental data. This study corroborates well the new kinetic model recently proposed for primary scalar active transport of small hydrophilic molecules involving ATP as the energy supply.

Picosecond ultrasonics study of metallic multilayers

Abstract A picosecond ultrasonics study of Cu/W superlattices in periods between 5 and 20 nm has been performed. Determination of acoustic echoes, observed over 200 ps, showed a softening of the longitudinal elastic constant for the shortest periods. High frequency oscillations were also detected over the first 20 ps. These oscillations, with frequencies extending up to 0.810 THz, are tentatively attributed to localized surface modes in the first zone center frequency gap.